1. Field of the Invention
The present invention relates to an electronic component in which surface mount devices mounted on a wiring board are covered with a cover member, and a manufacturing method of the electronic component. More particularly, the present invention relates to an electronic component which can be miniaturized and which can have a reduced height due to the improved structure of a cover member, and a manufacturing method of the electronic component.
2. Description of the Related Art
Known technologies are disclosed in Japanese Unexamined Patent Application Publication No. 6-350280 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 8-250615 (Patent Document 2), and Japanese Unexamined Patent Application Publication No. 11-354663 (Patent Document 3).
Patent Document 1 discloses a hybrid IC with a metal shield case mounted on a ceramic board. The hybrid IC includes a ceramic board having a wiring pattern, and electronic components, such as a microcomputer, a transistor, and an IC, mounted on either side or both sides of the ceramic board. The ceramic board has a plurality of connection terminals extending perpendicularly downward from the outer peripheral edge thereof. The metal shield case made by bending both ends of a rectangular plate is mounted on the upper surface of the ceramic board, so as to block external noise. The shield case also functions as a sucking surface for picking up the hybrid IC for placement on a mother board.
Patent Document 2 discloses a ceramic package for a semiconductor chip, the ceramic package including a ceramic cover member having a box-like shape. The ceramic package for the semiconductor chip includes a ceramic package base on which a semiconductor chip is mounted, and the ceramic cover member for covering the package base. A copper plate layer is provided on the inner surface of the cover member, a sealing solder layer is provided on a sealed surface with a copper plate layer interposed therebetween, and the copper plate layer on the sealed surface is electrically connected to the copper plate layer on the inner surface. Also, a ground electrode is provided on the sealed surface of the package base, and the package base is sealed, with the sealing solder layer of the cover member interposed.
Accordingly, the copper plate layer on the sealed surface of the cover member is electrically connected to the ground electrode of the package base to function as a ground electrode layer, and the copper plate layer on the inner surface of the cover member functions as an electromagnetic shield layer.
Patent Document 3 discloses a sealing cover member for a semiconductor device and its manufacturing method. The sealing cover member has a multilayered structure including a plurality of ceramic layers. A shield layer is provided at an inner layer by wide area printing with paste. The back surface of the ceramic cover member and a board body facing the back surface are bonded by a binder paste, and thus, the cavity of the board body is sealed. Chip components may be mounted on both front and back surfaces of the ceramic cover member.
However, with the configuration disclosed in Patent Document 1, when the shield case has a reduced thickness so as to reduce the height of the electronic component such as the hybrid IC, it is difficult to perform accurate processing of the shield case, for example, by bending because the shield case is made of metal. In addition, the shield case may be markedly deformed due to an external force applied to the shield case during picking up. Generally, as shown in a part FIG. 17A, a load is applied to the electronic component 1 from the upper surface of a shield case 2 by a jig used for characteristic screening of an electronic component 1, and a terminal electrode 4 provided on the back surface of a board body 3 of the electronic component 1 electrically comes into contact with a measurement terminal P of a measurement instrument as shown in FIG. 17B. At this time, if the shield case is markedly deformed, then the upper surface of the shield case 2 bends due to the load, and the shield case 2 comes into contact with an element component 5, such as a chip component. This may cause a short-circuit. In addition, since the distance between the shield case 2 and the element component 5 varies, the characteristic value of the element component 5 is changed. Accordingly, it is difficult to accurately measure the characteristic value of the electronic component 1. In some cases, an acceptable product may be erroneously identified as a defective product and removed, or a defective product may be erroneously identified as an acceptable product and shipped. To avoid this, a thin resin film may be provided on the inner surface of the shield case 2 as an insulating layer. However, the provision of the resin film increases the manufacturing cost. In addition, the reliability of the electronic component may be deteriorated if the resin film becomes detached.
With the configuration disclosed in Patent Document 2, since the ceramic cover member has the box-like shape, if the thickness of the ceramic cover member is reduced so as to reduce the height of the electronic component, waviness may be generated at a top portion 2A because of the difference between the behavior of shrinkage in a plane direction of the top portion 2A and that of an outer wall 2B of the box-like cover member 2 during firing, as shown in FIGS. 18A and 18B. Due to the waviness, the thickness of the top portion 2A of the cover member 2 is not substantially reduced, and consequently, the reduction in height of the electronic component may not be sufficient. In addition, when the electronic component is mounted on the mother board, it is difficult to suck the electronic component with the cover member 2 interposed therebetween, during picking up because the top portion 2A of the cover member 2 is not flat. This may cause defective mounting. FIG. 18A is a partial cross-sectional view when a plurality of cover members are manufactured at a time, and FIG. 18B is a cross-sectional view when the cover members are cut into individual pieces.
With the configuration disclosed in Patent Document 3, the cavity of the electronic component is sealed with the flat cover member. Thus, the configuration may not be applied to an electronic component having no cavity. Accordingly, with this configuration, a cavity is required on the side of the wiring board on which the cover member is disposed. This may increase the number of steps in the manufacturing procedure, thereby increasing the manufacturing cost. Further, when the chip component is mounted on the cover member, soldering and reflowing must be performed two times for mounting the chip component on the cover member, and for mounting the cover member on the wiring board. When the cover member is mounted on the wiring board, however, the chip component previously mounted on the cover member may be detached due to remelting of the solder. Accordingly, breaking may occur, and in some cases, the solder may become an alloy or be brittle due to recrystallization of the solder. Thus, the reliability of the solder connection portion may be seriously deteriorated.